The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Known electric motors include permanent magnet electric motors and other induction motors that transform electric power to mechanical torque. Permanent magnet electric motors may be multiphase interior permanent magnet (IPM) electric motors that include permanent magnets buried within a rotor core and aligned longitudinally with an axis of rotation. Known stators include an annular stator core and a plurality of electrical windings. Known stator cores include a plurality of radial inwardly projecting tooth elements that are parallel to a longitudinal axis of the electric motor and define an inner circumference of the stator. Contiguous radial inwardly projecting tooth elements form radially-oriented longitudinal slots. Electrical windings are fabricated from strands of suitable conductive material, e.g., copper or aluminum, and are woven or otherwise arranged into coil groups that are inserted into the radially-oriented slots between the tooth elements. Electrical windings are arranged electrically in series in circular fashion around the circumference of the stator core, with each electrical winding associated with a single phase of the electric motor. Each coil group of the electrical windings provides a single pole of a single phase of motor operation. The quantity of radially-oriented slots in the stator core is determined based upon the quantity of phases and poles of the electrical wiring windings for the electric motor. Thus, a three-phase, two-pole motor will have electrical windings that are configured as six coil groups. Current flow through the electrical windings is used to generate rotating magnetic fields that act on a rotor to induce torque on a shaft of the rotor.
Known rotors for permanent magnet electric motors include a rotor core attached to a rotating shaft that defines an axis of rotation, and have a plurality of rotor magnets positioned around the circumference near an outer surface of the rotor core, with each rotor magnet aligned longitudinally with the axis of rotation.
Known electric motors include an air gap between tooth elements of a stator and an outer surface of a rotor. An air gap is a design feature that physically separates the rotor and stator part to accommodate manufacturing tolerances and facilitate assembly, and address other known factors. An air gap is preferably minimized, as an increased air gap correlates to reduced magnetic flux and associated reduced output torque of the electric motor.
When electric current flows through the stator windings, a magnetic field is induced along the electrical windings to act upon the rotor magnets of the rotor element. The magnetic field induces torque on the rotating shaft of the rotor. When the magnetic field induces sufficient torque to overcome bearing friction and any induced torque load on the shaft, the rotor rotates the shaft.
Design of electric motors includes factors related to magnetics, mechanics, thermodynamics, electronics, acoustics, and material sciences. It is known that performance requirements, packaging constraints and costs impose constraints on motor design that affect design features. Known performance requirements include maximum motor torque output, torque ripple, and cogging torque, which affect noise, vibration, and harshness performance of the electric motor. Known permanent magnet electric motors have flux distribution due to the permanent magnets and the armature magneto-motive forces that is non-sinusoidal with respect to the angular rotor position.
Permanent magnet electric motors including IPM motors may be used in vehicle propulsion applications because of their high efficiency and high power density. An electric motor may be sized according to expected load profiles, e.g., duty cycles of the vehicle and overall efficiency and power loss. Operating temperature of permanent magnet electric motor, e.g., winding temperature is dependent upon an actual operating load and duty cycle. In an operating regime including prolonged operation at peak output power, an electric motor may overheat. Overheating may accelerate aging and deterioration of insulation on stator windings and demagnetize permanent magnets, thus degrading motor performance and reducing electric motor life.
Known IPM motors may monitor winding temperature using direct measurement systems, e.g., by installing thermocouples or thermistor devices within stator windings. Temperature measurement systems add components, increase wiring harness complexity and require signal monitoring hardware and software. Known thermal models may use motor operating parameters to estimate winding temperature and have associated estimation errors.